1. Field of the Invention
This invention relates to a process for catalytically rearranging aromatic sulfilimines.
2. Description of the Prior Art
The preparation of ortho-(alkylthiomethyl) anilines from the corresponding anilines via sulfilimine intermediates is known. Claus, Tetrahedron Letters, p. 3607 (1968), describes the preparation of aromatic sulfilimines from anilines and dimethylsulfoxide in the presence of P.sub.2 O.sub.5 in a base such as triethylamine. Claus, however, discloses thermally rearranging these sulfilimines to ortho-(methylthiomethyl) anilines. See also, Gassman, Tetrahedron Letters, p. 497 (1972) and Johnson, Tetrahedron Letters, p. 501 (1972). Gassman discloses the use of N-t-butylanilines to generate N-t-butyl-N-chloro anilines, generally employing an alkyl-hypochlorite, and subsequently sulfilimine salts with dimethyl sulfide. Upon treatment with a basic catalyst under anhydrous conditions the sulfilimine salts are converted to N-substituted ortho-(methylthiomethyl) anilines. Vilsmaier, Tetrahedron Letters, p. 625 (1972) describes the reaction of anilines with dimethyl sulfide and N-chlorosuccinimide to form sulfilimine hydrochloride salts. Vilsmaier here does not teach the rearrangement of the sulfilimine or its salt. Another method of preparation of sulfilimine salts is disclosed in Claus and Vilsmaier, Tetrahedron Letters 31, p. 505 (1975). This article, like the previous Vilsmaier article, discloses the reaction of anilines with dimethyl sulfide in the presence of N-chlorosuccinimide to form the sulfilimine hydrochloride salt. In the Claus and Vilsmaier reference the sulfilimine hydrochloride salt is neturalized with aqueous caustic but Claus and Vilsmaier do not disclose the rearrangement of the sulfilimine produced by this process. See also Gassman U.S. Pat. Nos. 3,894,034, 3,954,797, 3,960,962, 3,985,765 and 4,035,375. The Gassman patents generally relate to the preparation and essentially anhydrous rearrangement of sulfilimine salts using basic catalysts to produce ortho-(methylthiomethyl) anilines. Claus, et al., Phosphorus and Sulfur, 1, pp. 11, 18 (1976) (and references cited therein) and U.S. Pat. No. 4,172,095 describe sulfilimine rearrangement in the presence of alcohols such as ethanol or t-butanol.
The prior art processes for preparing ortho-(alkylthiomethyl) anilines via the sulfilimine route generally exhibit a number of drawbacks which make them undesirable for commercial scale conversion processes. These prior art sulfilimine formation and rearrangement reactions proceed satisfactorily at the laboratory scale but they employ reagents which are expensive, often dangerous, and difficult to work with on a larger scale. One of the most serious of these drawbacks is the generally held requirement for processing under anhydrous conditions and utilizing dry bases such as tertiary amines. Moreover, the rearrangement of sulfilimines to ortho-(alkylthiomethyl) anilines was thought to require high temperatures, the presence of alcohols or dry basic catalysts such as triethylamine.
Accordingly, it is an object of the present invention to provide a process for the catalytic rearrangement of aromatic sulfilimines which substantially avoids the drawbacks of the prior art.
It is another object of this invention to provide a process for catalytically rearranging aromatic sulfilimines using novel rearrangement catalysts.
It is also an object of the present invention to provide a new class of sulfilimine rearrangement catalysts that are easier to use and generally more efficient than the alcohols and organic bases used by the prior art.